Protective face masks or respirators for the human face are well known. Persons wearing such respirators often have a need to communicate with one another, particularly in emergency situations. Respirators not equipped with voice amplification mechanisms are typically provided with a valve through which the wearer both exhales and speaks. Sound transmitted through such valves, however, is somewhat muffled, and thus various communications systems have been developed for respirators to improve sound transmission capabilities.
For example, U.S. Pat. No. 4,901,356 to Bauer employs separate microphone and amplifier assemblies to provide a voice transmission system which may be used with a protective respirator. U.S. Pat. No. 5,138,666 to Bauer et al. provides a system for a similar purpose which utilizes a combined microphone and amplifier assembly. In each of these systems, the microphone and the amplifier are located outside of the protective mask.
Locating the microphone outside of the mask, however, is disadvantageous in that the microphone must pick up the wearer's voice after it has passed through the valve in its muffled state. In addition, the volume level of the voice prior to amplification is diminished, and must be raised by increasing the gain of the amplifier, which increases power consumption. Further, by placing both the microphone and the amplifier outside the mask, acoustic isolation of these items is difficult and thus acoustic feedback problems are encountered.
By placing the microphone inside the mask and acoustically isolating it from the amplifier electronics, sound quality is improved, less feedback problems are experienced, and, because a decreased amplifier gain is required, power consumption is reduced. Because most respirator voice amplification devices are battery operated, power consumption is an important consideration.
Its known to have microphones contained within the mask and amplifier electronics located outside the mask. For example, UK Patent Application GB 2 165 721A discloses an internal microphone and external amplifier electronics. However, in such an embodiment, the microphone must be separately attached to the inside of the mask. Moreover, even with the microphone separated from the amplifier assembly by a couple inches, because the amplifier is attached to the mask and therefore remains in relatively close proximity to the amplifier/speaker, acoustic feedback problems are likely to persist.
Accordingly, it is an object of the present invention to provide a voice transmission assembly which may be easily incorporated into an existing respirator and which provides clear sound and low power consumption, having an internal microphone which need not be separately mounted in the mask. It is a further object to provide such an adaptive system which permits the amplifier/speaker assembly to be remotely mounted away from the mask and the microphone contained therein to eliminate acoustic feedback problems.